The present invention relates to a process for the production of a spray-dried, pourable washing aid containing nonionic tensides of the ethoxylated alcohol type and having a powder density of from 300 g/l to 550 g/l.
Washing aids are products which, on their own, are unable to satisfy all the demands made of a heavy-duty detergent, but which may be incorporated as additives in ready-made detergents or used as detergency boosters in conventional washing processes to enable special washing problems to be more effectively solved. Nonionic tensides or surface-active agents have proved to be effective detergency boosters, particularly for removing obstinate stains.
Normally, modern detergents already contain nonionic tensides in quantities of from 3 to 20% by weight. However, the view generally held among experts is that detergents of low specific gravity, i.e. with a powder density of less than 600 g/l, which contain more than 8 to 10% by weight of these generally liquid to semi-solid, more or less tacky nonionic tensides cannot be satisfactorily produced by spray drying of aqueous concentrates (slurries). Although German Published Application DE-AS No. 17 92 434 to Coffey et al., corresponding to British patent GB-PS No. 1,232,009 to Coffey et al., describes a process for producing granular detergents containing from 5 to 20% of nonionic tensides by spray drying of an aqueous slurry, the detergents in question contain from 25 to 60% and, according to the Examples, from 40 to 52% of tripolyphosphate, a phosphate content which is now regarded as unreasonably high. In addition, the production process is complicated by the fact that the tripolyphosphate used for preparing the slurry has to be partially prehydrated beforehand. In spite of this, it is not possible in practice to incorporate much more than 15% by weight of nonionic tensides in the powder so long as importance is attributed to adequate fluidity of the powder particles. In addition, there were serious objections to the spray drying of powders of high tenside, particularly nonionic tenside, content on account of the danger of dust explosions and intense pluming caused by nonionic material entrained in the off-gases of the spray towers. For this reason, the relevant specialist and patent literature warns against processing mixtures such as these of high tenside content in hot spray towers and, instead, proposes applying relatively high percentages of nonionic tenside to preformed carrier particles by spray granulation.
Thus, in the process according to DE-AS No. 10 98 132 to Pfrengle et al., for example, the nonionic tenside is sprayed in a proportion of up to 60% onto a spray-dried and, therefore, particularly adsorbent sodium tripolyphosphate, resulting in the formation of a granulate having a powder density of less than 550 g/l. However, since the end product contains more than 30% by weight and preferably more than 40% by weight of phosphate, it no longer complies with the requirements which an environmentally acceptable product can be expected to satisfy.
Similar processes are described in U.S. Pat. Nos. 3,838,072 to Smith, et al., 3,849,327 to DiSalvo, et al.I, 3,886,098 to DiSalvo, et al.II, and 3,926,827 to Mangeli. A granular carrier material is prepared by spray drying of a slurry containing sulfonate tensides, soap and large quantities of inorganic salts acting as carrier material, such as sulfates, silicates and phosphates, and is subsequently sprayed with nonionic tenside in a mixer. It is said to be possible in this way to produce powders having a powder density of from 300 to 800 g/l and a nonionic tenside content of up to 25% by weight. In order with such a high nonionic tenside content as this to prevent the granules from sticking to one another, the granules have to be aftertreated (powdered) with an adsorbent, such as silica (Aerogel.RTM.) or carboxymethyl cellulose. A 3-stage production process such as this is relatively complicated.
In addition, detergents having a powder density of at least 500 g/l, which consist of substantially spherical particles of a certain size and which are apparently capable of adsorbing up to 30% by weight of nonionic tensides, are known from U.S. Pat. No. 4,269,722 to Joshi, et al. In this case, too, a highly adsorbent carrier grain has to be prepared beforehand by a special spraying process and subsequently treated in a mixer with the nonionic tenside. These products are also rich in phosphate and relatively expensive on account of the several stages involved in their production.
Another disadvantage of the multistage processes generally known as "spray mixing processes" lies in the fact that the preformed carrier grains undergo a certain degree of abrasion during their subsequent treatment with nonionic tenside in a mixer, resulting in the formation of fines. In addition, the nonionic tensides are capable, by virtue of their tacky properties, of cementing granules together to form relatively large agglomerates. Accordingly, the material being treated changes its grain spectrum, which is frequently undesirable and necessitates an additional sifting process.
In addition, it is known from DE-OS No. 24 18 294 to Saran, et al., and from DE-PS No. 2 837 504 to Kubersky, et al., that nonionic tenside mixtures having a special composition and nonionic tensides having a special constitution can be sprayed onto a water-soluble carrier salt, more particularly perborate, and that the granulate obtained may be subsequently incorporated in a ready-made washing powder. In these cases, however, special nonionic compounds have to be used within restricted prototype formulations. In addition, it is difficult to produce pourable granulates containing more than 15% by weight of nonionic tenside.